The Seattle-based coffee company says a digital tip function will be added to its mobile payment application starting next summer. A similar option will also be available on Square, a new payment app that Starbucks customers will be able to use starting in November.

Starbucks plans to switch its processing of debit and credit card payments to mobile payments start-up Square, the two companies said Tuesday, in a deal will help establish two-year-old Square as a bona fide player in the industry.

Square makes it much easier for even the smallest retailers to accept credit cards: The mobile payment firm offers easy to use hardware that plugs right into iPhones or Androids. But at least part of its new high price tag probably derives from the fact that its founder, Jack Dorsey, also co-founded Twitter.

The smartphone revolution is about to upend another business: credit card processing. With Google's new Android app that allows you to literally pay by phone, and Square's new hardware that turns any iPhone into a transaction processor, your plastic could become obsolete.